Pacific Northwest Research Station

Threatened northern spotted owls are an important indicator species for old-growth forest ecosystems and face threats from habitat loss and competition with barred owls. Now, scientists have identified another challenge for spotted owls: increased breeding dispersal distance. In other words, adult spotted owls must travel farther to find mates and suitable breeding habitat, which could influence their survival.

Breeding dispersal is the movement of birds between different breeding locations, which they typically do to find new mates, locate better habitat, and escape threats from competition or predation. Breeding dispersal is inherently risky because travelling to find new habitat can leave birds open to new threats and expends valuable energy. So, if a species’ breeding dispersal increases, there is likely an important change in their environment influencing this behavior.

Spotted owls are traveling farther, more often than 30 years ago

A new study published in The Condor: Ornithological Applications reports that spotted owls are now travelling farther and more often to breed than they have in the past. Julie Jenkins, a postdoctoral research wildlife biologist with the U.S. Forest Service’s Pacific Northwest Research Station, worked with her colleagues to study changes in the breeding dispersal of spotted owls in Oregon and Washington between 1990 and 2017. During that time, spotted owls started travelling, on average, 1.5 miles farther in Oregon and nearly 6 miles farther in Washington to locate new breeding territories. Not only are the owls travelling farther overall now than they were 30 years ago, but the rate of repeat dispersals is also increasing, suggesting the behavior is not necessarily an isolated response.

Greater dispersal distance is an additional stress on the threatened spotted owl

“We found a concurrent increase in barred owl presence during the study period that suggests their competition was influencing spotted owl breeding dispersal. This was a change from previous findings that found spotted owl dispersal distance was influenced by social structure and habitat availability in the 90s,” Jenkins said. “It appears that barred owls are now compounding those effects.”

Increased competition from barred owls, combined with previous habitat loss and population declines, means that spotted owls often travel farther to find suitable replacement territories—another potential stress on an already threatened population.  

“The fact that spotted owls have to travel farther to breed is a concern because changes in dispersal behavior can affect survival rates, particularly if longer movements mean increased exposure to low-quality habitat outside of forest reserves,” Jenkins said. “This information is one more piece toward understanding the ongoing challenges facing conservation efforts for the spotted owl.”

The study was done in collaboration with Oregon State University, the U.S. Geological Survey, the U.S. Bureau of Land Management, Olympic National Park, and the U.S. Forest Service’s Rocky Mountain Research Station.